1. Technical Field
The present invention relates to a polarizing plate and an optical display apparatus including the same.
2. Description of the Related Art
A polarizing plate generally includes a polarizer having a polarizing function, and a protective film attached to one or both sides of the polarizer to protect the polarizer. According to the type of optical display apparatus to which the polarizing plate is mounted, a retardation compensation film, a bonding layer, an adhesive layer, a surface treatment layer, or the like may be additionally stacked on the protective film of the polarizing plate. The protective film may serve to provide retardation and optic axis correction in addition to providing polarizer protection.
As a protective film for a polarizing plate, triacetyl cellulose (TAC) films have been used. Since TAC films have high glass transition temperatures (Tg) and are manufactured by casting, the films exhibit stable length shrinkage in a mechanical direction (MD) or transverse direction (TD). Further, the TAC films are manufactured without a stretching process, and thus exhibit no heat shrinkage.
Recently, polyethylene terephthalate (PET) films have been used in an effort to diversify protective films for polarizers. Substitute films, such as PET and the like, are stretched films and have relatively high MD or TD elongation. On this account, PET films may exhibit thermal shrinkage and expansion behavior. Further, PET films have lower glass transition temperatures than TAC films, and thus may exhibit thermal shrinkage, which in turn causes distortion of the optical axis of a polarizer during manufacture of the polarizing plate, thereby lowering the degree of polarization.
For this reason, technologies have been developed to control the MD or TD shrinkage of PET films. Although the basic physical properties or bending properties of the films can be controlled by controlling MD or TD shrinkage, such control is represented by shrinkage in the mechanical/transverse directions, and does not prevent optical axis distortion occurring during manufacture or driving of the polarizing plate.